There is known a technology that performs stereo-matching for a plurality of images of a target object captured around a vehicle; this technology enables a disparity between matched correspondence points of respective right and left images for each point of the target object to be generated, thus calculating, based on the disparity for each point of the target object, a depth distance of each point of the target object relative to the vehicle.
For example, Japanese Patent Application Publication No. 2016-81108, which will be referred to as a published patent document, discloses an object detection apparatus.
The object detection apparatus disclosed in the published patent document includes a grouping unit, an optical flow obtaining unit, a matching unit, and an object detector.
The grouping unit divides pixel regions constituting an image captured around a vehicle into plural pixel-region groups in accordance with depth distance information about each pixel region.
The optical flow obtaining unit obtains optical flows for each of target object.
The matching unit matches each of the optical flows with a corresponding one of the pixel-region groups in accordance with a positional relationship between the corresponding one of the optical flows and the corresponding one of the pixel-region groups. Each optical flow matched with a corresponding one of the pixel-region groups will be referred to as a matched optical flow.
The object detector detects how the at least one target object been moving in accordance with the matched optical flows.
The larger the number of optical flows for a target object matched with a corresponding pixel-region group is, the more the accuracy of detecting how the target object has been moving is improved. An increase in the number of optical flows matched a corresponding pixel-region group however causes the processing load of the matching unit to increase.
From this viewpoint, the matching unit disclosed in the published patent document is configured to make smaller the number of optical flows for a target object to be matched with per unit area of each of selected pixel-region group that have a smaller average depth distance.
That is, the published patent document describes that a decrease in each of the selected pixel-region groups that have a smaller average depth distance may not contribute greatly to reduction of the detection accuracy of how the target object for each of the selected pixel-region groups has been moving.
The published patent document therefore describes that, for this reason, it is possible to achieve both maintenance of the detection accuracy of the target objects being high, and reduction in the processing load of the matching unit.